Forb Biomass Research Articles

Grazing Exclusion Effect on Soil and Vegetation Properties in Imam Kandi Rangelands, Iran

Most of the rangeland of Urmia in Iran is degraded and will require considerable reclamation to achieve a desirable state. The aim of this study was to evaluate the effects of 14 years of grazing exclusion on vegetation and soil properties in Imam Kandi rangelands. Sampling in both grazing exclosure and grazed areas were conducted using a systematic randomized sampling method. Six 100-m long transects were randomly located in each area and ten 1 × 1 m sampling plots were located along each transect. Within each plot, species presence, canopy cover, species yield, and plant densities were measured. Soil cores were taken in the center of each vegetation sampling plot at 0–30 cm and 30–60 cm depths. Organic matter, nitrogen content, the amounts of phosphorus and potassium, electrical conductivity (ECe), pH, the percentage of CaCO3, and soil texture were determined for each sample. Results indicate differences in plant canopy cover, species composition, and yield between the grazing exclosure and the control site. All plant growth forms at the exclusion site differed from those at the grazed site. Biomass of perennial grasses, perennial forbs and annual forbs was greater at the exclusion site than at the grazed site, and biomass of annual grasses and shrubs at the control site was greater than at the exclusion site. Overall grazing exclosure site improved the vegetation composition and soil quality parameters ECe, pH, organic matter, nitrogen, phosphorus, and potassium content relative to the grazed site.

Short-term vegetation response to wildfire in the eastern Sierra Nevada: Implications for recovering an endangered ungulate

We studied short-term changes in vegetation for two years following a summer wildfire on the winter ranges of Sierra Nevada bighorn sheep (Ovis canadensis sierrae). Forbs dominated burned areas and shrubs dominated unburned areas. Green forage (new-growth of all forage classes) biomass rebounded quickly; within two years green forage biomass was equal in burned and unburned areas, although total forage biomass remained greater in unburned areas. Plants in the burn had slightly higher crude protein but equivalent digestibility and phenology as plants in unburned areas. This, in combination with the shift toward more forb biomass, likely increased forage quality in burned areas. Forage models developed from ground-based measures of biomass performed better than the NDVI and were able to capture changes in forage composition, emphasizing the importance of field sampling to model vegetation. Based on microhistological analyses of fecal pellets, Sierra Nevada bighorn sheep whose winter ranges were extensively burned consumed more forbs than those with less burned habitat. Visibility was greater in burned areas compared with unburned areas, suggesting that burns may decrease predation risk from stalking predators. In conclusion, wildfire may have beneficial effects for Sierra bighorn by increasing forb availability, forage quality and visibility.

Response of mule deer to habitat modification near natural gas development

Mule deer ( Odocoileus hemionus ) are known to shift habitat use in response to environmental modifications, including those associated with energy development. Their specific behavioral responses, however, and capacities to habituate to particular aspects of energy development have not been effectively studied. We examined mule deer response to habitat alteration near natural gas wells in Las Animas County, Colorado, USA in 2008—2010, an area experiencing development for extraction of natural gas. We created 10-1 ha openings in forests adjacent to 10 wells by removing standing trees in 2008, with concomitant establishment of 10 1-ha control sites adjacent to the same wells. On each site, we estimated deer use, indexed by pellet density, before and after tree removal. Concurrently, we measured plant production, cover, nutritional quality, species composition and biomass removed by deer and other large herbivores. Species richness and diversity and graminoid and forb cover and biomass increased on cut sites following tree removal. Use increased following tree removal on cut and control sites, but was greater on cut sites in 2010. Herbivores removed negligible quantities of vegetation on control sites in both years, suggesting that control sites may have been used primarily for concealment. Mule deer demonstrated the behavioral capacity to habituate to habitat modifications and other environmental changes associated with development for the extraction of energy. Managing forage and habitat availability appears to have the potential to affect the type of response and degree of habituation by mule deer to such development.

Plant phosphorus nutrition indicators evaluated in agricultural grasslands managed at different intensities

A precise assessment of the phosphorus (P) nutrition status of plants is necessary for an efficient P management in agricultural grasslands. Plant mineral analysis is a tool to identify the nutrition status of grasslands and several P indicators derived thereof are available. However, the interpretation of plant P indicators in grassland samples is complex due to variation in botanical composition, changing nutrient concentrations during growth and interactions between nutrients. The aim of this study was to compare indicators on the P nutrition status of plants and eventually to improve their application in agricultural grasslands. We studied three agricultural grassland types in Switzerland that were managed at different intensity either for high biodiversity or high forage production. Each grassland type was for 5–25 years subjected to treatments of low, recommended or high rates of P, nitrogen (N) and potassium (K) fertilizer. The recommended P rates ranged from 15 to 48kgPha−1year−1. We measured plant P, N and K concentrations in the aboveground biomass of grasses, legumes and forbs. The evaluated P indicators were: P concentration, N:P and K:P ratios and the P nutrition index (PNI). The PNI is calculated as P concentration divided by the linear relationship describing optimal sward P concentration as a function of N concentration (PNI=100P/(0.06×5N+1.5)). We observed significant yield reduction compared to the expected yield only when one or more nutrients were omitted from fertilization. Fertilizer P input higher than recommended did not significantly increase yields above the yield expected for the respective management and altitude. Under P limiting conditions, forbs and legumes had significantly higher P concentrations than grasses. Additionally, the proportion of legumes affected the P indicators integrating N. Therefore, we used the P indicators in the grass fraction, which was always the main botanical fraction. In grasses all P indicators differentiated between P fertilized and non-P-fertilized treatments. Concentrations of P from 2.1 to 3.0mgg−1 indicated sufficient P supply, while yield was reduced at lower and not increased at higher concentrations, suggesting luxurious P consumption. Our results for N:P and K:P suggested optimal ranges of 5.5–9.0 and 6.0–10.5, respectively. The PNI showed a clear differentiation between deficient, sufficient or surplus fertilizer inputs. For the precise and correct interpretation of the plant P nutrition status in agricultural grasslands under different management, we propose to use the PNI in the grass fraction. Finally, the interpretation of the indicators was valid for the agricultural grasslands managed at different intensities in spite that the grass fraction was composed by different species.

Changes in plant functional groups and species diversity under three grassland using modes in typical grassland area of Inner Mongolia, China

Aims Our objectives were to reveal changes in plant functional groups and species diversity under three grass-land using modes in typical steppe of Inner Mongolia, China. Methods Three plots in similar habitats were selected from the Hulunbeier steppe area of the Hui River National Nature Reserve: an meadow plot (controlled utilization), pasture plot (moderate utilization) and public pasture plot (severe utilization). Plots were 250 m × 250 m and consisted of three sample belts separated by 20 m. Each sample belt had eight 1 m × 1 m sample plots. Important findings There were differences in species composition and community characteristics of the func-tional groups. Shrubs and sub-shrubs combined were significantly different (p 0.05) among the plots, with the highest value in meadow. Perennial grasses were significantly different (p 0.05). Annual and biennial herbs combined had significant differences (p 0.05), with the highest value in the public pasture. The public pasture also had the highest percentage of the xerophyte functional group (50%) and the lowest mesoxerophyte and meso-phyte (19%), and differences were significant (p 0.05) among the plots. The biomass of shrubs and sub-shrubs were lower in all plots. The combined biomass of perennial grasses and forbs decreased with the increase in grassland use intensity among meadow, pasture and public pasture, while the combined biomass of annual and biennial herbs increased. With the increase in use intensity, the community structure and composition tended to become simplified and susceptible to change. Richness and diversity were lowest in the pasture and highest in meadow. Differences in evenness were not significant. The use of meadow contributed to improving the health of the grassland, but pasture and public pasture exhibited over-grazing phenomena. The public pasture had degraded significantly because of the uncertainty about property responsibility and ineffective management.

Response of Elk to Habitat Modification Near Natural Gas Development

Elk (Cervus elaphus) are known to shift habitat use in response to environmental modifications, including those associated with various forms of energy development. The specific behavioral responses underlying these trends, however, have not been effectively studied. To investigate such effects, we examined elk response to habitat alteration near natural gas wells in Las Animas County, Colorado, USA in 2008-2010. We created 10 1-ha openings in forests adjacent to 10 operating natural gas wells by removing standing timber in 2008, with concomitant establishment of 10 1-ha control sites adjacent to the same wells. On each site, we estimated elk use, indexed by pellet density, before and after timber removal. Concurrently, we measured plant production and cover, nutritional quality, species composition and biomass removed by elk and other large herbivores. Species richness and diversity, graminoid and forb cover, and graminoid and forb biomass increased on cut sites following tree removal. Differences were greater in 2010 than in 2009, and elk and deer removed more plant biomass in 2010 than 2009. Elk use of cut sites was 37% lower than control sites in 2009, but 46% higher in 2010. The initially lower use of cut sites may be attributable to lack of winter forage on these sites caused by timber removal and associated surface modification. The increased use of cut sites in 2010 suggested that elk possessed the behavioral capacity, over time, to exploit enhanced forage resources in the proximity of habitat modifications and human activity associated with maintenance of operating natural gas wells.

Host selectivity, haustorial anatomy and impact of the invasive parasite Parentucellia viscosa on floodplain vegetative communities in Japan

The parasitic plant Parentucellia viscosa has been introduced recently to the Japanese floodplain. Because of its parasitic nature and high fecundity, P. viscosa may well become a major plant invader with a significant impact on floodplain ecosystems. Thus, a knowledge of the host selectivity of P. viscosa will not only provide basic biological information, but will also contribute to the understanding of floodplain vegetation conservation. We evaluated the host selectivity by comparing the observed numbers of haustoria with those expected from the relative below-ground biomass. In addition, we examined the haustorial anatomy to determine whether haustoria are functional, and compared the above-ground biomass of three functional plant groups (grasses, legumes and nonleguminous forbs) in intact and parasite removal quadrats. We found that haustoria were nonrandomly distributed amongst host species, suggesting host preference for Poaceae and Fabaceae. In addition, haustoria attached to certain forbs did not penetrate into the stele. The above-ground biomass of grasses and legumes was increased significantly by the removal of P. viscosa, but the biomass of forbs did not change significantly. These results suggest that host preference depresses the performance of Poaceae and Fabaceae, thus affecting the competitive relationships among plants, meaning that P. viscosa may pose a serious threat to indigenous endangered legumes and grasses. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 69–78.

Effects of Liming on Forage Availability and Nutrient Content in a Forest Impacted by Acid Rain

Acidic deposition and subsequent forest soil acidification and nutrient depletion can affect negatively the growth, health and nutrient content of vegetation, potentially limiting the availability and nutrient content of forage for white-tailed deer (Odocoileus virginianus) and other forest herbivores. Liming is a mitigation technique that can be used to restore forest health in acidified areas, but little is known about how it affects the growth or nutrient content of deer forage. We examined the effects of dolomitic limestone application on the growth and chemical composition of understory plants in an acidified forest in central Pennsylvania, with a focus on vegetative groups included as white-tailed deer forage. We used a Before-After-Control-Impact study design with observations 1 year before liming and up to 5 years post-liming on 2 treated and 2 untreated 100-ha sites. Before liming, forage availability and several nutrients were below levels considered optimal for white-tailed deer, and many vegetative characteristics were related to soil chemistry. We observed a positive effect of liming on forb biomass, with a 2.7 fold increase on limed sites, but no biomass response in other vegetation groups. We observed positive effects of liming on calcium and magnesium content and negative effects on aluminum and manganese content of several plant groups. Responses to liming by forbs and plant nutrients show promise for improving vegetation health and forage quality and quantity for deer.

Different inter-annual responses to availability and form of nitrogen explain species coexistence in an alpine meadow community after release from grazing.

Plant species and functional groups in nitrogen (N) limited communities may coexist through strong eco-physiological niche differentiation, leading to idiosyncratic responses to multiple nutrition and disturbance regimes. Very little is known about how such responses depend on the availability of N in different chemical forms. Here we hypothesize that idiosyncratic year-to-year responses of plant functional groups to availability and form of nitrogen explain species coexistence in an alpine meadow community after release from grazing. We conducted a 6year N addition experiment in an alpine meadow on the Tibetan Plateau released from grazing by livestock. The experimental design featured three N forms (ammonium, nitrate, and ammonium nitrate), crossed with three levels of N supply rates (0.375, 1.500 and 7.500gNm-2 yr-1 ), with unfertilized treatments without and with light grazing as controls. All treatments showed increasing productivity and decreasing species richness after cessation of grazing and these responses were stronger at higher N rates. Although N forms did not affect aboveground biomass at community level, different functional groups did show different responses to N chemical form and supply rate and these responses varied from year to year. In support of our hypothesis, these idiosyncratic responses seemed to enable a substantial diversity and biomass of sedges, forbs, and legumes to still coexist with the increasingly productive grasses in the absence of grazing, at least at low and intermediate N availability regimes. This study provides direct field-based evidence in support of the hypothesis that idiosyncratic and annually varying responses to both N quantity and quality may be a key driver of community structure and species coexistence. This finding has important implications for the diversity and functioning of other ecosystems with spatial and temporal variation in available N quantity and quality as related to changing atmospheric N deposition, land-use, and climate-induced soil warming.

Is regular mowing the most appropriate and cost-effective management maintaining diversity and biomass of target forbs in mountain hay meadows?

Conservation of grassland biodiversity is a key issue in the EU agro-biodiversity policy. We assessed the effects of yearly mowing on target forb biomass in years with contrasting precipitation (2006–2007) in mountain fen and dry-mesophilous hay meadows in NE-Hungary. We hypothesised: (i) Species richness and biomass of target forbs is higher in mown than in abandoned stands. (ii) Mowing has more an effect on the biomass of target forbs, graminoids and litter than precipitation.Mowing increased the species richness of forbs and target forbs. The biomass of forbs and target forbs was not affected by mowing because of the specific responses of certain forbs. The majority of target species were supported, but tall forbs (Succisa pratensis; Lathyrus pratensis) were suppressed by mowing. Precipitation affected only the amount of litter in dry-mesophilous meadows and forb biomass in fen meadows. In the dry year, the biomass of target forbs decreased but the proportion of the species did not change. Our results showed that mowing is necessary to maintain overall plant biodiversity in hay meadows by removal of graminoid biomass and litter, but not all target forbs were favoured by regular yearly mowing. Decreased mowing frequency (mowing in every second or third year) on the entire meadow or temporarily changing mosaics of mown and unmown stripes might be the most suitable management option for maintaining the highest biodiversity of forbs.

Developing custom fire behavior fuel models from ecologically complex fuel structures for upper Atlantic Coastal Plain forests

Currently geospatial fire behavior analyses are performed with an array of fire behavior modeling systems such as FARSITE, FlamMap, and the Large Fire Simulation System. These systems currently require standard or customized surface fire behavior fuel models as inputs that are often assigned through remote sensing information. The ability to handle hundreds or thousands of measured surface fuelbeds representing the fine scale variation in fire behavior on the landscape is constrained in terms of creating compatible custom fire behavior fuel models. In this study, we demonstrate an objective method for taking ecologically complex fuelbeds from inventory observations and converting those into a set of custom fuel models that can be mapped to the original landscape. We use an original set of 629 fuel inventory plots measured on an 80,000ha contiguous landscape in the upper Atlantic Coastal Plain of the southeastern United States. From models linking stand conditions to component fuel loads, we impute fuelbeds for over 6000 stands. These imputed fuelbeds were then converted to fire behavior parameters under extreme fuel moisture and wind conditions (97th percentile) using the fuel characteristic classification system (FCCS) to estimate surface fire rate of spread, surface fire flame length, shrub layer reaction intensity (heat load), non-woody layer reaction intensity, woody layer reaction intensity, and litter–lichen–moss layer reaction intensity. We performed hierarchical cluster analysis of the stands based on the values of the fire behavior parameters. The resulting 7 clusters were the basis for the development of 7 custom fire behavior fuel models from the cluster centroids that were calibrated against the FCCS point data for wind and fuel moisture. The latter process resulted in calibration against flame length as it was difficult to obtain a simultaneous calibration against both rate of spread and flame length. The clusters based on FCCS fire behavior parameters represent reasonably identifiable stand conditions, being: (1) pine dominated stands with more litter and down woody debris components than other stands, (2) hardwood and pine stands with no shrubs, (3) hardwood dominated stands with low shrub and high non-woody biomass and high down woody debris, (4) stands with high grass and forb (i.e., non-woody) biomass as well as substantial shrub biomass, (5) stands with both high shrub and litter biomass, (6) pine-mixed hardwood stands with moderate litter biomass and low shrub biomass, and (7) baldcypress-tupelo stands. Models representing these stand clusters generated flame lengths from 0.6 to 2.3m using a 30kmh−1 wind speed and fireline intensities of 100–1500kWm−1 that are typical within the range of experience on this landscape. The fuel models ranked 1<2<7<5<4<3<6 in terms of both flame length and fireline intensity. The method allows for ecologically complex data to be utilized in order to create a landscape representative of measured fuel conditions and to create models that interface with geospatial fire models.

Impact of nitrogen addition on plant community in a semi-arid temperate steppe in China

Increased nitrogen (N) deposition will often lead to a decline in species richness in grassland ecosystems but the shifts in functional groups and plant traits are still poorly understood in China. A field experiment was conducted at Duolun, Inner Mongolia, China, to investigate the effects of N addition on a temperate steppe ecosystem. Six N levels (0, 3, 6, 12, 24, and 48 g N/(m⋅a)) were added as three applications per year from 2005 to 2010. Enhanced N deposition, even as little as 3 g N/(m⋅a) above ambient N deposition (1.2 g N/(m⋅a)), led to a decline in species richness of the whole community. Increasing N addition can significantly stimulate aboveground biomass of perennial bunchgrasses (PB) but decrease perennial forbs (PF), and induce a slight change in the biomass of shrubs and semi-shrubs (SS). The biomass of annuals (AS) and perennial rhizome grasses (PR) accounts for only a small part of the total biomass. Species richness of PF decreased significantly with increasing N addition rate but there was a little change in the other functional groups. PB, as the dominant functional group, has a relatively higher height than others. Differences in the response of each functional group to N addition have site-specific and species-specific characteristics. We initially infer that N enrichment stimulated the growth of PB, which further suppressed the growth of other functional groups.

Fire and grazing influence food resources of an endangered rock-wallaby

Context Fire and grazing have complex and interacting impacts on food resources available to endangered herbivores and can potentially be manipulated as part of conservation strategies. Aims We examined the interacting impacts of fire and grazing on the food resources available to a colony of endangered brush-tailed rock-wallabies (Petrogale penicillata) to test fire as a potential management tool. Methods We conducted two manipulative experiments using a repeated-measures split-block design. We measured the effects of grazing and strategic burning on total vegetation biomass and on particular plants selected by rock-wallabies. In the first experiment we measured the impact of rock-wallaby grazing alone. In the second experiment we measured grazing impacts by both rock-wallabies and potentially competitive sympatric macropods. Grazing was manipulated with three treatments: grazed (open), ungrazed (fenced) and procedural control (half fence). Key results In both experiments, burning resulted in greater above-ground biomass of plants selected by rock-wallabies. The response of different plant functional groups to fire was staggered, with forb biomass peaking early and browse biomass increasing above unburnt levels a year after burning. Conclusions Despite the limited grazing pressure exerted by the small colony of rock-wallabies in Experiment 1 we detected a negative grazing effect on forbs growing after fire in burnt plots. In Experiment 2, grazing pressure was much more marked due to the high densities of sympatric macropods. In this case, while burning resulted in greater biomass of plants selected by rock-wallabies, grazing (predominantly by sympatric macropods) negated this effect. Implications Small patchwork burning can be a useful tool to improve food resources for brush-tailed rock-wallabies, with effects sustained over more than two years. However, when rock-wallabies are sympatric with possible competitor species, the grazing impacts of sympatric macropods may cancel out any benefits to rock-wallabies.

Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores

Productive tundra plant communities composed of a variety of fast growing herbaceous and woody plants are likely to attract mammalian herbivores. Such vegetation is likely to respond to different-sized herbivores more rapidly than currently acknowledged from the tundra. Accentuated by currently changing populations of arctic mammals there is a need to understand impacts of different-sized herbivores on the dynamics of productive tundra plant communities. Here we assess the differential effects of ungulate (reindeer) and small rodent herbivores (voles and lemmings) on high productive tundra vegetation. A spatially extensive exclosure experiment was run for three years on river sediment plains along two river catchments in low-arctic Norway. The river catchments were similar in species pools but differed in species abundance composition of both plants and vertebrate herbivores. Biomass of forbs, deciduous shrubs and silica-poor grasses increased by 40–50% in response to release from herbivory, whereas biomass of silica-rich grasses decreased by 50–75%. Hence both additive and compensatory effects of small rodents and reindeer exclusion caused these significant changes in abundance composition of the plant communities. Changes were also rapid, evident after only one growing season, and are among the fastest and strongest ever documented in Arctic vegetation. The rate of changes indicates a tight link between the dynamics of productive tundra vegetation and both small and large herbivores. Responses were however not spatially consistent, being highly different between the catchments. We conclude that despite similar species pools, variation in plant species abundance and herbivore species dynamics give different prerequisites for change.

Litter and graminoid biomass accumulation suppresses weedy forbs in grassland restoration

Accumulated biomass of sown species and litter plays an important role in success of restoration projects. We studied the effects of litter and graminoid biomass on species richness and biomass of early colonising forbs in former alfalfa fields sown with seed mixtures containing seeds of native grass species (Festuca pseudovina, Festuca rupicola, Poa angustifolia, Bromus inermis, 2005). The amount of litter, forbs and graminoids was measured in the first 3 years after sowing (2006–2008). Ten aboveground biomass samples (20 cm × 20 cm) per field were collected in June every year. We found significantly lower forb biomass in the second and third year, than in the first year after sowing. Litter and biomass of graminoids increased significantly during the study, and correlated negatively with the biomass and species richness of forbs. Mean scores of litter and graminoid biomass were two to three times higher in sown fields than in native grasslands. Our results suggest that the accumulation of litter and graminoid biomass is beneficial in suppression of weedy forbs, but in the long run it might also hamper the immigration of target species.

Nitrogen enrichment enhances the dominance of grasses over forbs in a temperate steppe ecosystem

Abstract. Chinese grasslands are extensive natural ecosystems that comprise 40 % of the total land area of the country and are sensitive to N deposition. A field experiment with six N rates (0, 30, 60, 120, 240, and 480 kg N ha−1 yr−1) was conducted at Duolun, Inner Mongolia, during 2005 and 2010 to identify some effects of N addition on a temperate steppe ecosystem. The dominant plant species in the plots were divided into two categories, grasses and forbs, on the basis of species life forms. Enhanced N deposition, even as little as 30 kg N ha−1 yr−1 above ambient N deposition (16 kg N ha−1 yr−1), led to a decline in species richness. The cover of grasses increased with N addition rate but their species richness showed a weak change across N treatments. Both species richness and cover of forbs declined strongly with increasing N deposition as shown by linear regression analysis (p &lt; 0.05). Increasing N deposition elevated aboveground production of grasses but lowered aboveground biomass of forbs. Plant N concentration, plant δ15N and soil mineral N increased with N addition, showing positive relationships between plant δ15N and N concentration, soil mineral N and/or applied N rate. The cessation of N application in the 480 kg N ha−1 yr−1 treatment in 2009 and 2010 led to a slight recovery of the forb species richness relative to total cover and aboveground biomass, coinciding with reduced plant N concentration and soil mineral N. The results show N deposition-induced changes in soil N transformations and plant N assimilation that are closely related to changes in species composition and biomass accumulation in this temperate steppe ecosystem.

Independent effects of arbuscular mycorrhiza and earthworms on plant diversity and newcomer plant establishment

Questions: How do arbuscular mycorrhiza and earthworms affect the structure and diversity of a ruderal plant community? Is the establishment success of newcomer plants enhanced by these soil organisms and their interactions? Methods: We grew a native ruderal plant community composed of different functional groups (grasses, legumes and forbs) in the presence and absence of arbuscular mycorrhizal fungi (AMF) and endogeic earthworms in mesocosms. We introduced seeds of five, mainly exotic, plant species from the same functional groups after a disturbance simulating mowing. The effects of the soil organisms on the native ruderal plant community and seedling establishment of the newcomer plants were assessed. Results: After disturbance, the total above-ground regrowth of the native plant community was not affected by the soil organisms. However, AMF increased plant diversity and shoot biomass of forbs, but decreased shoot biomass of grasses of the native plant community. Earthworms led to a reduction in total root biomass. Establishment of the introduced newcomer plants increased in the presence of AMF and earthworms. Especially, seedling establishment of the introduced non-native legume Lupinus polyphyllus and the native forb Plantago lanceolata was promoted in the presence of AMF and earthworms, respectively. The endogeic earthworms gained more weight in the presence of AMF and led to increased extraradical AMF hyphal length in soil. However, earthworms did not seem to modify the effect of AMF on the plant community. Conclusion: The present study shows the importance of mutualistic soil organisms in mediating the establishment success of newcomer plants in a native plant community. Mutualistic soil organisms lead to changes in the structure and diversity of the native plant community and might promote newcomer plants, including exotic species.

Decreasing Precipitation Variability Does Not Elicit Major Aboveground Biomass or Plant Diversity Responses in a Mesic Rangeland

Inter- (between years) and intra- (within year) annual variability of precipitation are high on rangelands. We used replicated rainout shelters in a southern tallgrass prairie ecosystem to decrease precipitation variability for 3 yr (1999–2001). We removed interannual variability in total precipitation plus either 1) interannual variability in the seasonal distribution of precipitation (seasonal distribution) or 2) all additional variability in precipitation, including within-year differences in precipitation (even distribution). Our objective was to determine if decreasing variability in precipitation elicits aboveground biomass and plant diversity responses. Aboveground biomass was harvested in June (peak biomass) and December (end of growing season). Plant species diversity, richness, and evenness were determined each June. Reducing precipitation variability had limited effects on total aboveground biomass, grass and forb biomass, and biomass of key species across the 3 yr of investigation. Species richness, species diversity, species evenness, and functional group richness and diversity all were similar across the precipitation treatments across years. Total aboveground biomass and biomass of the dominant C4 perennial grasses little bluestem (Schizachyrium scoparium) and Indiangrass (Sorghastrum nutans) generally were not responsive to the precipitation treatments. However, one species-specific response did occur with the annual forb firewheel (Gaillardia pulchella Foug.) displaying consistent increases in biomass in the seasonal distribution precipitation treatment across all 3 yr. This suggests that increased predictability of precipitation at a given stage of this species’s growth can elicit changes in productivity of a single species that are not manifest at the community level due to constraints of the dominant species. These findings indicate that the southern tallgrass prairie ecosystem is adaptable to changes in precipitation to result in relatively stable production that facilitates simpler predictions in response to altered precipitation regimes.

Carbon Addition as a Technique for Controlling Exotic Species in Pacific Northwest Prairies

Competition for soil resources is a driving force in plant community ecology. Therefore, amendments that alter soil resources should affect vegetation dynamics and are potential tools for controlling exotic species. We tested the effects of two types of carbon addition, sugar and activated carbon (AC), on an exotic-dominated grassland plant community. Sugar stimulates the microbial community and temporarily reduces plant available nitrogen (N), while AC adsorbs plant available N. Six experimental plots and three carbon treatments were used: sugar (1000 g m-2; 42% C), AC (420 g m-2; 100% C), and control. Treatments were applied in a split-plot design in spring 2008. Aboveground biomass, plant cover, species richness, and plant basal area were tracked for two growing seasons. Although total biomass was not affected by C addition, the distribution of biomass among life forms was affected: carbon addition reduced forb biomass but had no effect on grasses or legumes. Total cover was lower in sugar-treated plots, and sugar also altered the proportional composition of that cover by reducing the abundance of forbs, especially in the first year. Five species were particularly sensitive to sugar addition: Myosotis discolor, Sonchus asper, Taraxacum officinale, Valerianella locusta, and Vulpia bromoides. Sugar also reduced plant basal area in the first year. These results suggest that sugar and, to a lesser extent, AC could be useful management tools. Sugar could be applied to areas where herbicide use is undesirable, reducing the abundance of exotic forbs and providing a window of opportunity for native species establishment.

Fire severity affects vegetation and seed bank in a wetland

Questions: How does the severity of prescribed fires affect vegetation and seed bank in a wetland? Location: A fire-prone reed swamp in northern Japan (250 ha, 40°49′N, 141°22′E, <10 m a.s.l.). Methods: Vegetation, biomass and seed bank were monitored for the 2 yr after annual prescribed fires were discontinued. Plant communities were placed into three categories based on fire severity: high (H) – fire consumed litter completely; moderate (M) – fire removed standing litter but left wet fallen litter; and low (L) – fire incompletely removed standing litter and did not remove fallen litter. Soil samples were collected in autumn 2007 and early summer 2008, and germinable seed bank was investigated by greenhouse trials. Results: High fire severity increased diversity in the next growing season by the establishment of short herbs in the standing vegetation. The biomass of forbs and grasses was greater in H where Phragmites australis biomass was reduced. The density of seed bank was >30 000 seeds m−2 throughout all the treatments. Perennial plants were dominant in the vegetation, while annuals, biennials and rushes were dominant in the seed bank. Small seeds were more abundant in the soil than in the litter. Qualitative and quantitative similarities between seed bank and the vegetation were low, and tended to be higher in H. Conclusions: Fire contributed to the development of diverse standing vegetation via the positive effects on seed bank dynamics, and can be considered a tool to maintain species-rich marshes.